The present invention relates to a process for producing a materials with reduced grain sizes, and can be used, for example, to produce sputtering target materials (i.e., physical vapor deposition target materials, and it is to be understood that in the context of this document the terms xe2x80x9cphysical vapor depositionxe2x80x9d and xe2x80x9csputteringxe2x80x9d can be used interchangeably). In particular applications, the sputtering target materials can comprise titanium, aluminum or copper. The sputtering target materials can hereinafter be referred to as a xe2x80x9ctarget materialsxe2x80x9d.
The quality of a thin film formed on a substrate by a sputtering method can be influenced by the surface roughness of a target material used for the sputtering. When protrusions having a larger size than a certain level are present on the surface of the target material, an abnormal discharge (so-called micro-arcing) can be caused at the protrusions. The abnormal discharge can result in macroparticles being scattered out from the surface of the target material, and deposited onto the substrate. The deposited macroparticles can cause blobs on the thin film and result in short circuiting of semiconductor thin film circuits. The deposited macroparticles are usually called xe2x80x9cparticlesxe2x80x9d or xe2x80x9csplatsxe2x80x9d.
The surface roughness of a target material can have a correlation to a crystal grain size of the target material. The finer the crystal grain size, the smaller the surface roughness of the target material. Accordingly, by reducing the size of crystal grains existing within the target material, it is possible to prevent the generation of the xe2x80x9cparticlesxe2x80x9d, thereby allowing better quality thin films to be formed than can be formed from targets having larger grain sizes.
Numerous materials can be utilized as target materials, including, for example, copper, aluminum and titanium. In particular applications, target materials can comprise alloys or other metallic mixtures, with exemplary mixtures comprising one or more of copper, aluminum or titanium. Target materials can also comprise so-called xe2x80x9chigh purityxe2x80x9d forms of particular metallic materials, with exemplary targets being from 99.99% pure to greater than 99.9999% pure in one or more of titanium, aluminum and copper.
Several methods have been proposed for forming improved target constructions. In Japanese Patent Application Laid-Open (KOKAI) No. 11-54244 (1999), there has been proposed a target material composed of titanium and having an average crystal grain size of 0.1 to 5 xcexcm. The target material is produced by hydrogenating titanium, subjecting the titanium to plastic working while maintaining an xcex1-phase or (xcex1-xcex2)-phase crystal structure thereof, and then dehydrogenating and heat-treating the titanium. However, a production method which includes hydrogenation and dehydrogenation treatments can be problematic from the industrial viewpoint. Consequently, it would be desirable to develop an alternative process for producing a titanium target material.
Another method proposed for forming an improved target construction is set forth in Japanese Patent Application Laid-Open (KOKAI) No. 10-330928 (1998). Such proposes a sputtering target material made of an aluminum alloy and containing crystal grains having an average diameter of not more than 30 xcexcm. The target material is produced by subjecting a raw metal material to plastic working, and then rapidly heating the metal material to a re-crystallizable temperature. The rapid heating utilizes an average temperature increase ramp rate of 100xc2x0 C./minute. A difficulty with the production method of KOKAI No. 10-330928 is that it can require a special heating method to accomplish the rapid heating, with exemplary special heating methods including an infrared irradiation method, an electromagnetic induction heating method or an immersion method using either a salt bath or a bath of low-melting alloy such as solder. Thus, the production method can be difficult to incorporate cost-effectively into industrial processes. Accordingly, it would be desirable to develop alternative processes for producing aluminum target materials.
The invention encompasses methods of reducing grain sizes of materials, and in particular applications encompasses methods of reducing grain sizes of titanium-comprising materials, aluminum-comprising materials, and/or copper-comprising materials. The invention further encompasses methods of forming sputtering targets. In a particular embodiment, the invention encompasses a method for producing a sputtering target material in which a metallic material is subjected to plastic working at a processing percentage of at least 5% utilizing a processing rate of at least 100% per second (i.e., 100%/second). In particular applications the metallic material comprises one or more of aluminum, copper and titanium.